Plasma-enhanced Chemical Vapor Deposition Technique Research Articles

Characteristics of industrially manufactured amorphous hydrogenated carbon (a-C:H) depositions on high-density polyethylene

Industrially high-density polyethylene (HDPE) was successively covered by two types of amorphous hydrogenated carbon (a-C:H) films, one more flexible (f-type) and the other more robust (r-type). The films have been grown by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique with acetylene plasma. The surface morphology of both types has been studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Contact angle measurements and Raman spectroscopy analysis were done to investigate the surface wettability and carbon chemical composition. Both types display similar morphology and grain growth pattern. Contact angle measurements revealed surface modifications especially at smaller r-depositions with a pronounced hydrophilic behavior. The f-depositions remain almost unchanged. For high r-depositions a rearrangement of the carbon composition is found and related to a growth of sp2 hybridized carbon species, despite of the hydrogen content. The values of the average grain heights are correlated to the values of the average grain areas and are localized in a limited area, indicating a given regularity during the different carbon depositions.

Band Gap Tailoring of TiO2 Nanowires by Nitrogen Doping Under N2/Ar Plasma Environment.

Glancing angle deposited TiO2 nanowires (NWs) were doped with nitrogen (N) using plasma-enhanced chemical vapour deposition technique, under the treatment of N2/Ar plasma. A red shift (- 0.51 eV) in the main band transition and oxygen defect related transition (-2.1 eV) was observed for the N doped TiO2 nanowires. The interstitial nitrogen introduces mid-gap levels N (2P) above the O (2P) in the TiO2 forbidden gap. The photoluminescence measurement revealed a small red shift of -7 nm of anatase band gap from N doped TiO2 nanowires due to radiative recombination of carriers from conduction band to the N (2P) trap state. The low frequency Raman peaks at 304 cm(-1) (acoustical phonons with LA mode), 618 cm(-1) (optical phonons with LO modes) and the high frequency peak at 832 cm(-1) was observed from Ti-O-N due to the partial replacement of oxygen molecules by nitrogen into TiO2, during the doping process.

Surface morphology and grain analysis of successively industrially grown amorphous hydrogenated carbon films (a-C:H) on silicon

Silicon (100) has been gradually covered by amorphous hydrogenated carbon (a-C:H) films via an industrial process. Two types of these diamond-like carbon (DLC) coatings, one more flexible (f-DLC) and one more robust (r-DLC), have been investigated. Both types have been grown by a radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) technique with acetylene plasma. Surface morphologies have been studied in detail by atomic force microscopy (AFM) and Raman spectroscopy has been used to investigate the DLC structure. Both types appeared to have very similar morphology and sp2 carbon arrangement. The average height and area for single grains have been analyzed for all depositions. A random distribution of grain heights was found for both types. The individual grain structures between the f- and r-type revealed differences: the shape for the f-DLC grains is steeper than for the r-DLC grains. By correlating the average grain heights to the average grain areas for all depositions a limited region is identified, suggesting a certain regularity during the DLC deposition mechanisms that confines both values. A growth of the sp2 carbon entities for high r-DLC depositions is revealed and connected to a structural rearrangement of carbon atom hybridizations and hydrogen content in the DLC structure.

Field emission current from a junction field-effect transistor

Fabrication of a titanium dioxide/carbon nanotube (TiO2/CNT)-based transistor is reported. The transistor can be considered as a combination of a field emission transistor and a junction field-effect transistor. Using direct current plasma-enhanced chemical vapor deposition (DC-PECVD) technique, CNTs were grown on a p-typed (100)-oriented silicon substrate. The CNTs were then covered by TiO2 nanoparticles 2–5 nm in size, using an atmospheric pressure CVD technique. In this device, TiO2/CNT junction is responsible for controlling the emission current. High on/off-current ratio and proper gate control are the most important advantages of device. A model based on Fowler–Nordheim equation is utilized for calculation of the emission current and the results are compared with experimental data. The effect of TiO2/CNT hetero-structure is also investigated, and well modeled.

Development of an Optically Transparent Silicon Based Technology Platform for Biological Analysis

A prototype optical structure suitable for advanced biological investigation has been successfully manufactured using plasma-enhanced chemical vapor deposition and deep reactive-ion etching techniques. Our approach to the design and fabrication of the structure is such that it can easily be integrated onto a lab-on-a-chip cell positioning platform, combining the use of integrated circuit technology with optimal in situ analysis of cells through the substrate using high-resolution inverted microscope systems. This paper describes the concept, design, fabrication, and optical characterization of a transparent window and corresponding via, which extends from the top surface to bottom surface of a silicon wafer. The effectiveness of the platform is demonstrated in multicolor fluorescence imaging of cells, cultured on-chip, using an inverted, confocal microscope.

Influence of substrate bias voltage on the microstructure of nc-SiOx:H film**Project supported by the Key Basic Research Project of Hebei Province, China (Grant No. 12963930D), the Natural Science Foundation of Hebei Province, China (Grant No. F2013201250), and the Science and Technology Research Projects of the Educational Department of Hebei Province, China (Grant No. ZH2012030).

Amorphous silicon oxide containing nanocrystalline silicon grain (nc-SiOx:H) films are prepared by a plasma-enhanced chemical vapor deposition technique at different negative substrate bias voltages. The influence of the bias voltage applied to the substrate on the microstructure is investigated. The analysis of x-ray diffraction spectra evidences the in situ growth of nanocrystalline Si. The grain size can be well controlled by varying the substrate bias voltage, and the largest size is obtained at 60 V. Fourier transform infrared spectra studies on the microstructure evolutions of the nc-SiOx:H films suggest that the absorption peak intensities, which are related to the defect densities, can be well controlled. It can be attributed to the fact that the negative bias voltage provides a useful way to change the energies of the particles in the deposition process, which can provide sufficient driving force for the diffusion and movement for the species on the growing surface and effectively passivate the dangling bonds. Also the larger grain size and lower band gap, which will result in better photosensitivity, can also be obtained with a moderate substrate bias voltage of 60 V.

Microstructure and electrochemical properties of nitrogen-doped DLC films deposited by PECVD technique

Nitrogen-doped diamond-like carbon (N-DLC) films were synthesized by glow discharge plasma enhanced chemical vapor deposition (PECVD) using a hybrid ion beam system. The influence of nitrogen incorporation on the microstructure and electrochemical properties of N-DLC films was investigated by scanning probe microscopy, Raman spectroscopy, X-ray photoemission spectroscopy and cycle voltammetry. Regardless of the deposition parameters, the surface of all the deposited films is very smooth. Raman spectra show that ID/IG increases from 0.6 to 1.04 with the substrate bias voltage increases. XPS results identify that carbon is bonded with nitrogen and the substrate bias makes no distinct contribution to the N content in the films, even the N-DLC film at bias of −550V has the lowest N–O bonds concentration and the highest C–N bonds concentration. The film electrodes show the wide potential windows range over 4V, lower background currents in strong acid media. At the bias of −550V, the N-DLC film electrode not only exhibits the ΔEp at 209mV and Ipox/Ipred at 0.8778 in K3Fe(CN)6 solution, respectively, but also illustrates a nearly reversible electrode reaction. The mechanism of electroproperties is discussed in terms of the atomic bond structures and diffusion process.

Variable corrosion behavior of a thick amorphous carbon coating in NaCl solution

The present work investigates a thick amorphous multi-layer carbon coating fabricated by a plane hollow cathode plasma-enhanced chemical vapor deposition technique.

Effects of protons within SiO2 solid-state electrolyte on performances of oxide electric-double-layer thin film transistor

SiO2-based solid state electrolyte films are deposited at room temperature by using the plasma-enhanced chemical vapor deposition (PECVD) technique. An electric-double-layer (EDL) effect has been observed. Then, indium-zinc-oxide thin-film transistors (IZO TFTs) are fabricated by using such SiO2 films as dielectrics in a self-assembling process through a shadow mask. The IZO films for source/drain electrodes and channel are deposited on the nanogranular SiO2 film by RF sputtering the IZO target in an Ar ambient. Such TFTs exhibit a good performance at an ultralow operation voltage of 1.5 V, with a high field-effect mobility of 11.9 cm2/Vs, a small subthreshold swing of 94.5 mV/decade, and a large current on-off ratio of 7.14×106. Effects of protons in the SiO2-based solid state electrolyte films on the electrical performances of the IZO TFTs are also studied. It is observed that a big EDL capacitance can be obtained for SiO2 films dipped in pure water, as a result of the fact that there are more protons in such SiO2 films. Because of the migration of protons in SiO2 electrolytes, an anti-clockwise hysteresis is observed on the transfer curve. Moreover, a bigger hysteresis is observed at a higher gate voltage scan rate. Gate bias stressing stabilities are also studied the shifts in threshold voltage are observed to obey a stretched exponential function.

CVD growth of carbon nanofibers

This review summarizes the growth and structural properties of carbon nanofibers (CNFs) using microwave plasma-enhanced chemical vapor deposition (MPCVD) technique and metal particles as the catalysts. The reaction gases were hydrocarbon and H2. Depending on catalyst materials, different types of CNFs have been grown. A four-step growth mechanism, namely adsorption, desorption, diffusion, and precipitation, is proposed to demonstrate the growth of CNFs under those conditions. The growth of carbon nanohelices (CNHs) is explained by the hexahedron morphology of the catalyst particles and difference in growth velocities on crystallographic surface planes. The appeared and potential applications of CNFs are outlined at the end of this review.

CVD growth of carbon nanofibers

This review summarizes the growth and structural properties of carbon nanofibers (CNFs) using microwave plasma-enhanced chemical vapor deposition (MPCVD) technique and metal particles as the catalysts. The reaction gases were hydrocarbon and H2. Depending on catalyst materials, different types of CNFs have been grown. A four-step growth mechanism, namely adsorption, desorption, diffusion, and precipitation, is proposed to demonstrate the growth of CNFs under those conditions. The growth of carbon nanohelices (CNHs) is explained by the hexahedron morphology of the catalyst particles and difference in growth velocities on crystallographic surface planes. The appeared and potential applications of CNFs are outlined at the end of this review.

A stable silicon anode based on the uniform dispersion of quantum dots in a polymer matrix

We propose a novel approach to the fabrication of silicon-containing anodes for lithium-ion batteries. Our approach is based on a liquid dispersion comprising of silicon quantum dots, carbon nanotubes and polyvinylpirrolidone (PVP) as a polymer additive. Coating of this dispersion onto copper foil followed by annealing in inert atmosphere allows the realization of a structure with good electrical conductivity, high specific surface area and with a carbon-based coating preventing the direct contact between the silicon particles and the electrolyte. This structure maintains a specific charge capacity of approximately 1000 mAh g−1 for 200 cycles and reaches a coulombic efficiency of 99.8%. The addition of PVP is a simple and scalable way of realizing, after annealing, a carbon-based matrix which surrounds the silicon particles and which greatly enhances the stability of the battery. The proposed process is based on commercially available carbon nanotubes, on silicon quantum dots which are produced using a scalable plasma-enhanced chemical vapour deposition technique, and is compatible with large area coating and processing techniques. The fabrication protocol described in this contribution represents a step towards the successful commercial utilization of silicon-based nanomaterials for energy storage applications.

Maxwell-Garnett theory – a method to investigate the quality of SiOx coatings

For single-layer barrier coatings, the influence of coating defects of thin SiOx coatings on the barrier properties was investigated. Coating defects only originate from the coating process; they seem to form independently from the surface roughness of the substrate. The coatings were deposited in a roll-to-roll process (width 1 m) by using the plasma-enhanced chemical vapour deposition technique. The SiOx coatings, applied in this work, have thicknesses in the range of 30–50 nm with a carbon content of less than 1 at-%. They show an oxygen transmission rate of 1·3 ± 0·4 cm3/(m2 day bar) at best. The focus of this research is to investigate the influence of plasma pressure on the coating defects and therefore to the barrier properties. In order to identify nanosized coating defects inside the coating, the Maxwell-Garnett theory was used. The defect volume was indirectly calculated with the help of ellipsometric measurement data. The Maxwell-Garnett theory is a very fast method to investigate the quality of barrier coatings.

Characterization of microcrystalline silicon thin film solar cells prepared by high working pressure plasma-enhanced chemical vapor deposition

Using the high working pressure plasma-enhanced chemical vapor deposition (HWP-PECVD) technique, the hydrogenated microcrystalline silicon (μc-Si:H) films for photovoltaic layers of thin film solar cells was investigated. The $\pmb{\mu \mathrm{c}-\mathrm{Si}:\mathrm{H}}$ films were deposited on surface textured fluorine-doped tin oxide (FTO) glass substrates at 100 Torr in a 100 MHz very high frequency (VHF) plasma of gas mixtures containing He, H2, and SiH4. It was found that an optimum ratio of the H2/SiH4 flowrate existed for growing a homogenous microcrystalline through the whole film without amorphous incubation layer. When an intrinsic $\pmb{\mu \mathrm{c}-\mathrm{Si}:\mathrm{H}}$ thin film was deposited at n-i-p single junction solar cell, the cell performances were dependent on with or without an amorphous incubation layer. With an amorphous incubation layer, the open circuit voltage $(\mathrm{V}_{\mathrm{oc}})$ of cell was 0.8V, which was typical cell property of hydrogenated amorphous silicon (a-Si:H). On the other hand, at the optimum ratio of the H2/SiH4 flow-rate, μc-Si:H single cell responding an infrared light showed the Voc of 0.49 V. Intrinsic hydrogenated microcrystalline silicon (μc-Si:H) thin film, exhibiting the photovoltaic performance (Eff: 7.2%, $\pmb{\mathrm{V}_{\mathrm{oc}}:0.49\mathrm{V}, \mathrm{J}_{\mathrm{sc}}:23\mathrm{mA}/\mathrm{cm}^{2}}$ , FF:64%) was able to be successfully fabricated.

Microwave plasma CVD-grown graphene–CNT hybrids for enhanced electron field emission applications

The growth and electron emission characteristics were investigated from a hybrid structure of multiwalled carbon nanotubes (MWCNTs) and multilayer layer graphene (MLG) deposited on silicon substrate coated with iron catalyst and an interlayer of aluminium. The hybrid structures were synthesized in a two-step process by microwave plasma-enhanced chemical vapour deposition technique. The formation of MWCNTs takes place by absorption and precipitation of carbon radicals into the catalyst particles. Thereafter, ample carbon forms MLG on tip of the MWCNTs resulting in a MLG-MWCNTs hybrid nanostructure. MLG was observed to grow branching out of the tips and sidewalls of the MWCNTs and is expected to attach by Van der Walls bonds. Transmission electron microscopy and micro-Raman spectroscopy confirmed the crystalline nature of the hybrid structures. Electron emission studies were carried out using a diode-type field emission setup. The enhancement factor was found to be ~3,500 for bare MWCNTs, ~4,070 to ~5,000 for hybrid structures and ~6,500 for N-doped MLG-MWCNTs hybrid structures. Modification in the defects structure and enhancement of emission sites are suggested to be responsible for the increase of the field emission characteristics.

Synthesis of Nanostructure Carbon Films Deposited by Microwave Plasma-Enhanced Chemical Vapor Deposition Technique at Room Temperature

This paper reports the synthesis of nanostructure carbon (ns-carbon) films deposited by microwave plasma-enhanced chemical vapor deposition (MW PECVD) technique at low pressure and room temperature. ns-carbon films have been characterized by scanning electron microscopy, electron dispersive x-ray spectroscopic analysis, atomic force microscopy, Raman spectroscopy, X-ray diffraction, UV-visible spectroscopy and high-resolution transmission electron microscopy. The shape of nanostructure is changing from granular to sheet-like structure when the pressure increased from 55 to 110 mTorr.

Experimental Investigation of Microstructure and Piezoresistive Properties of Phosphorus-Doped Hydrogenated Nanocrystalline Silicon Thin Films Prepared by PECVD

This paper presents an experimental investigation of microstructure and piezoresistive properties of phosphorus-doped hydrogenated nanocrystalline silicon (nc-Si:H) thin films. The phosphorus-doped nc-Si:H thin films (5% doping ratio of PH3 to SiH4) were deposited by plasma enhanced chemical vapor deposition (PECVD) technique. The microstructure and surface morphology of the deposited thin films was characterized and analyzed with Raman spectroscopy and atomic force microscopy (AFM), respectively. The piezoresistive properties of the deposited thin films were investigated with a designed four-point bending-based evaluation system. In addition, the influence of temperature on the piezoresistive properties of these thin films was evaluated with the temperature coefficient of resistance (TCR) measurements from room temperature up to 80°C. The experimental results show that phosphorus-doped nc-Si:H thin films prepared by PECVD technique are a two-phase material that constitutes of nanocrystalline silicon and amorphous silicon, and they present a granular structure composed of homogeneously scattered nanoclusters formed by nanocrystalline silicon grains (6nm). Moreover, phosphorus-doped nc-Si:H thin films exhibit negative GF at room temperature and show good thermal stability from room temperature up to 80°C, and the value of GF and TCR is about-31 and-509ppm/°C, respectively. These features could make phosphorus-doped nc-Si:H thin films act as a promising material for piezoresistive-based MEMS sensor.

The role of PECVD hard coatings on the performance of industrial tools

The advantages of the application of hard coatings, which are well knownfor cutting tools, are to a much lesser extent explored for casting, extrusion, molding and forming tools. Increasing the lifetime of these tools is an important task in surface engineering because of complex loading conditionsand often complicated tool geometry. The plasma-enhanced chemical vapor deposition (PECVD) technique is well suited to deposit hard coatings onto large dies and moulds. The aim of this study was to discuss deposition processes suitable for coating of the often large three-dimensional molds and dies used in metal forming. Furthermore, results obtained using different hard coatings in industrial applications for several case studies like aluminum pressure die-casting; plastics injection molding and sheet metal forming are presented and discussed. For best coating performance, a careful optimization of both substrate pretreatment and coating deposition is necessary. The plasma-enhanced chemical vapor deposition (PECVD) technique shows advantages for these applications because of the high flexibility in pre-treatment using chemical etching and plasma-nitriding, because of its ability to coat large complexly shaped tools and because of the possibility of deposition of low-chlorine containing low-friction coatings.

The dielectric response of low-k interlayer dielectric material characterized by electron energy loss spectroscopy

In this study, the dielectric response of low-k dielectric materials has been characterized by electron energy loss spectroscopy. A widely accepted fast Fourier transform based Kramers–Kronig method (Johnson, 1975) [3] has been used to derive the high-frequency response of these materials. We used three different low-k dielectric materials to find out the effect of porosity and carbon content on the dielectric response of materials. Amorphous SiO2 and SiC:H samples are used for comparison. All samples were deposited by plasma-enhanced chemical vapor deposition technique. A Lorentzian-based oscillator model has been used to determine the eigen-energy of excitations by fitting the measured loss function. The model is specially designed to let all oscillator parameters move freely and find their most probable position by using a least square fitting analysis procedure. The band gap for amorphous SiO2 which corresponds to the first absorption peak in the imaginary part of dielectric function is found to be at around 9eV. We observed that in the case of dense low-k material, there appears a finite density of states (DOS) inside the band gap of SiO2, whereas the inclusion of porosity into dense low-k network diminishes the in-gap DOS and widens the band gap to around 10eV.

The growth characteristics of microcrystalline Si thin film deposited by atmospheric pressure plasma-enhanced chemical vapor deposition

Microcrystalline silicon thin film was grown by atmospheric pressure plasma-enhanced chemical vapor deposition (AP-PECVD) technique with a cylindrical rotary electrode supplied with 150 MHz very-high-frequency power. The crystalline volume fraction could be controlled by changing the flow rate ratio of silane and hydrogen gas during AP-PECVD. We could also control it by regulating the substrate scanning speed. At low substrate scanning speed, the silicon film had a low crystalline volume faction and layer-by-layer structure with alternating layers of amorphous and microcrystalline Si. On the other hand, at high substrate scanning speed, silicon crystals of sizes 25 nm grew homogeneously throughout the whole film.